1. Field of the Invention
The present invention relates to an information signal processing apparatus for processing an information signal.
2. Description of the Related Art
An electronic still video system has heretofore been known as one example of an information signal processing apparatus for processing an information signal. The electronic still video system is arranged to record image signals on a plurality of recording tracks which are concentrically formed on a magnetic disk, and to select an arbitrary recording track from among the recording tracks formed on the magnetic disk and reproduce the image signal recorded on the selected recording track.
Such an electronic still video system is arranged to record the image signals on the recording tracks formed on the magnetic disk, in the state of analog signals. However, a new system has recently been proposed which is arranged to digitize an image signal obtained by photographing a subject by using a video camera or the like and store the digitized image signal in a memory card including a plurality of RAMs (random access memories).
To digitize the image signal and store the digitized image signal in the memory card, a memory card having a large storage capacity is needed since the digitized image signal has an enormous amount of information. However, since the memory card having the large storage capacity is costly, the above-described system is extremely expensive.
To cope with this problem, a system has recently been considered which is capable of storing a digitized image signal by using a hard disk unit which is lower in cost and larger in storage capacity than the aforesaid memory card.
In the system using such a hard disk unit, during the process of digitizing an image signal obtained by photographing a subject by means of a video camera or the like and recording the digitized image signal on a hard disk of the hard disk unit, it takes a predetermined time for the hard disk to reach its stable rotational speed which permits the hard disk unit to execute a storing operation. For this reason, some type of system adopts an arrangement which causes the hard disk to start its rotation before a start of a photographing-and-recording operation and, after the rotation has settled, holds the hard disk in a continuous rotating state during a wait for the start of the photographing-and-recording operation. Another type of system is provided with a buffer memory for temporarily storing a digitized image signal. In this type of system, image data corresponding to a photographed image is stored in the buffer memory, and after the rotation of the hard disk has settled, the image data stored in the buffer memory is read out and transmitted to the hard disk for storing purpose.
However, if the hard disk is held in the continuous rotating state during the wait for the start of the photographing-and-recording operation, power consumption will increase. As a result, if a portable, electric power source, such as a battery, is used to supply electricity to the electronic still video system, it will be necessary to frequently perform battery replacement. In the case of the buffer memory, during the continuous-shooting recording operation of continuously storing, on a hard disk, image signals continuously supplied from a video camera or the like, the buffer memory for temporarily storing image data may overflow, thereby interrupting the continuous-shooting recording operation at an intermediate time.
Still another type of system has recently been proposed in which a memory card provided with a memory device, such as a DRAM, an SRAM or an EEPRM, is used as a recording medium so that digitized still image and audio signals are recorded into the memory card.
However, the storage capacity of the memory card is limited because of the limited storage capacity per chip of the memory device or limits of the number of chips which can be mounted on a single memory card. In addition, since the memory device is more expensive than other recording media, it is economically difficult to utilize the memory card as a recording medium of large storage capacity.
In contrast, the aforementioned hard disk unit is known as a recording medium having a larger storage capacity than the memory card, and there has recently been provided a hard disk unit which is removably attachable to a main apparatus similarly to the memory card. If such a removable hard disk unit is used with an electronic still video camera as a recording medium, it is possible to construct comparatively inexpensively a system having a large storage capacity.
Various kinds of hard disk units are provided in accordance with various specifications such as recording capacity, weight, power consumption and recording speed. If the system is constructed so that plural kinds of hard disk units can be attached, it is possible to meet a variety of demands of users.
However, unlike the memory card having no mechanically moving part, the hard disk unit has the disadvantages that it is necessary to rotate a hard disk inside thereof during recording of an information signal and that a comparatively long time and electric power, which is larger than that during a normal rotating operation, are required during the start of rotation of the hard disk. For these reasons, a general arrangement is as follows: After the hard disk has been started up, it is held in a continuous rotating state for some time, and if a predetermined time elapses or the recording of the information signal is completed, the rotation of the hard disk is stopped.
However, if an electronic still video camera is constructed so that plural kinds of hard disk units can be attached as described above, since each kind of hard disk unit takes a different time to start up its hard disk, it is necessary to set the time interval during which the hard disk is held in a continuous rotating state after being started up, according to a particular hard disk unit from among the hard disk units attachable to the camera body of the electronic still video camera, that is, a hard disk unit which includes a hard disk having the longest start-up time and which consumes the largest amount of electric power during the start-up time of the hard disk.
For these reasons, the conventional system has the following problems. Even if a hard disk unit, which includes a hard disk having a short start-up time and which does not consume a large amount of electric power during the start-up time of the hard disk, is attached to the camera body, the hard disk is held in a continuous rotating state over a time interval longer than required with the result that a wasteful electric power is consumed. Since the aforesaid electronic still video camera is typically a portable apparatus which relies on a battery for its power supply, the wasteful power consumption remarkably decreases the time per battery during which the system can be operated to record information signals. As a result, if such an electronic still video camera is used to record still-image signals, the number of still-image pictures recordable per battery will be decreased.
Since the above-described electronic still video camera (electronic still camera) is arranged to perform digital recording, it is common practice to use a digital interface (I/F) as a transmission unit for transmitting data from the electronic still camera to external equipment.
Various types of digital I/Fs are available. However, since cameras are limited in body size, it is in many cases impossible to attach digital I/Fs of the type generally used with personal computers or the like to the cameras. For this reason, small digital I/Fs are generally used as transmission units dedicated to the cameras.
Alternatively, a method is proposed which utilizes a connector for a memory card as a digital I/F for transmission purpose.
Since electronic still cameras of the type using memory cards are provided with connectors for the memory cards, it is also possible to transmit data from such an electronic still camera to external equipment by using this general-purpose type of digital I/F.
However, in the case of an electronic still camera provided with both a transmission unit which is a digital I/F dedicated to the camera and a transmission unit which is a general-purpose digital I/F using a connector for a memory card, there is the problem that if both of the transmission units are connected to external equipment, it is impossible to determine which of the transmission units can be used to achieve optimum transmission.